site characterization for a new refinery in a disposal area for

Click to edit Master text styles

Bruno Pasqualini – Civil and Structural Engineering Section Head – Technip ItalyThe 5th International Conference on Geotechnical and Geophysical Site Characterisation Gold Coast, Queensland, Australia – 5 Sep 2016

Site characterization for a new refinery in a disposal area for bituminous residue

B. Pasqualini, E. Nicotera, A. Liberati, R. MarcelliniTechnip, Rome, ItalyP. Ascari & R. GalbiatiStudio Geotecnico Italiano, Milan, Italy

Site characterization for a new refinery in a disposal area for bituminous residue 2

INDEX

“Pitch pond”

Results of “traditional” site investigation

Trial Embankment

Settlements of trial embankment


«PITCH POND»

Adjacent to a plant to be expanded, there is a depression used in the past a s deposit of waste material.

This pitch pond area (60 ha) is covered by a thick (2÷6 m) layer of a material denominated “pitch”, constituted by a mix of natural soil and residual bituminous material from past industrial processes.


«PITCH POND»

• In the past, the “pitch pond” was used as disposal site for bituminous materials, mixed with the natural soil on site in various and uncontrolled percentages and methodologies.

• The thickness of this layer of “pitch” material is ranging from 2 to 6 m

• Consistency of pitch material ranges from relatively firm material (where the bituminous residuals have been mixed with high percentages of existing natural soils, constituted by silty sands and sandy silts), to almost “fluid” state, where very little, if no mixing at all, has been carried out.

• The pitch material overlies weathered limestone, becoming relatively intact at depth.


DEVELOPMENT OF REFINERY EXPANSION ON «PITCH POND»

• The basic project includes a capping of a clean, coarse grained material, 3÷4 m thick.

• In addition to the function of capping, this fill reduces issues related to future excavation/dewatering for foundation and underground services installation.

• The basic soil-mechanical design problem related to this solution is the assessment of the potential settlement due to the compressibility of “pitch” material.

• Assessment of settlements also defines the need and governs the design of soil improvement methods, and, in some case, requires the use of piles as foundation solutions.


DESIGN OF SITE INVESTIGATION• Peculiarity of materials: What is the reliability of usual correlations with “standard”

in situ tests (SPT, CPT, DMT, PLT) ?

• What are the techniques that would allow for “undisturbed” sampling of this material?

• What would be the representativeness of the sample behavior with respect to the site conditions?

Pending the above questions, the adoption of trial embankments has been chosen as main investigation method.

The stress increase, in the center of the embankment, should be approximatively constant through the depth of the pitch material, even considering its maximum thickness of 6 m, such that the settlements of the center of the embankment are representative of the effect of the construction of design final fill.

The investigation is complemented with “traditional” SPT, flat dilatometer and plate load tests.


RESULTS OF “TRADITIONAL” SITE INVESTIGATIONS - 1/4

The main purposes of traditional soil investigation in the pitch pond have been:

• To try to extend results of monitoring of trial embankments to the whole pond

• To give eventual hints about the behavior of the pitch material


RESULTS OF “TRADITIONAL” SITE INVESTIGATIONS – 2/4



• The general pattern of NSPT indicate a fairly tendency of increasing with depth.

• Maximum thickness of very soft pitch, having SPT of less than 5blows/30 cm, are in the order of 2-4m.

• The conditions found beneath the EM1 and EM2 can be considered as representative as a reasonably “lower bound” condition of the site.

• Using the correlation of Stroud (1974), and a multiplier coefficient of SPT equal to 5, one could obtain constrained modulus in the order of 1-2 MPa, for the lowest values of SPT.



• DMT interpretation using the correlation for clayey soils (Marchetti, 2001) gives values of constrained modulus M of few MPa, that are considered as reasonably representative of the expected values of this peculiar material

• Plate load test inferred operative Young modulus between 100 and 225 kPa is in the order of 5÷6 MPa.

• settlement recovery upon unloading is very small: a remarkable yielding of the pitch material took place


TRIAL EMBANKMENT- 1/3


TRIAL EMBANKMENT – 2/3

The dimensions of the trial embankments have been chosen such that the stress increase under the center of the embankment is similar to the one due to the construction of the design final fill.


TRIAL EMBANKMENT – 3/3

• Nos. 5 settlement plates have been installed at the base of each embankment.

• Specific weight of the embankments, measured during their construction, is 17.5 kN/m3


SETTLEMENTS OF TRIAL EMBANKMENTS – 1/3


SETTLEMENTS OF TRIAL EMBANKMENTS – 2/3

Embankments 1 and 2 show similar results, being the maximum settlement monitored in 25 weeks in the order of 65 to 70 mm.

Settlement vs time curves show two different slopes: • In the first part (about 10 days), settlement rate is

relatively fast and irregular. It is interpreted as the “consolidation” component, it the sense of a re-arrangement of the structure of the material due to the induced change in effective stress.

• Then the settlement curves show a more regular pattern. It is supposed that this second part is mainly governed by the viscous compressibility of the pitch material.


SETTLEMENTS OF TRIAL EMBANKMENTS – 3/3• The records show a tendency of an acceleration of the

settlement rate with log of time, for all points.

• Also, data suggest that the slope of the curves is lower for corner points, where the stress increase is also small (the value of Cαε results as dependent on effective stress level).

Both these findings are consistent with what found by Soleimanbeigi et al. (2014), A.,Soleimanbeigi and Tuncer(2015), and by Viyanant et al (2007), during the execution of oedometer tests on bituminous material mixed with sand or fly ashes, and on recycled asphalt shingle.

This long term behavior of pitch could not be estimated based on “traditional” soil investigation methods and monitoring of settlements of trial embankments is still on going.

www.technip.com

Thank You

site characterization for a new refinery in a disposal area for

Documents